In an image display device such as a liquid crystal display and an organic EL display of the related art has a space provided between a display module and a cover panel, and an air layer between the cover panel and the display module scatters light due to a difference in refractive index, and thus decreases illuminance and contrast. Therefore, measures have been taken against these problems by filling the space between the cover panel and the display module with an ultraviolet curable resin in the form of liquid. Further, for the same reasons, the ultraviolet curable resin is also used between cover glass and a touch panel and between the touch panel and the display module.
Patent Literature 1 below discloses a liquid ultraviolet curable composition, which contains a polyurethane acrylate, an isobornyl acrylate, and a photopolymerization initiator. However, a method of bonding with such a liquid ultraviolet curable resin has failed to avoid problems of bubbles entrained at the time of attachment and of the resin protruded from an end.
In a method of bonding a cover panel and a display module, a photocurable sheet-shape adhesive has been examined as one in which bubble entrainment or protrusion does not occur. Patent Literature 2 discloses, as a photocurable sheet-shape adhesive, a photocurable adhesive composition which contains a urethane (meth)acrylate oligomer having a specific molecular weight, a phenoxy resin, and a photopolymerization initiator. However, since a display module has used for a wide variety of devices, and the usage environments thereof have also gradually been harsh, when a device having a cover panel and a display module sealed with the composition disclosed in Patent Literature 2 is used under various conditions, it has been found that white turbidity occurs in an adhesive layer and transparency is impaired in the condition under high temperature and high humidity.